We plan to study further the effects of various substances other than divalent cations which may affect PTH secretion. These studies will utilize the canine model we have recently perfected for measuring PTH secretion directly in vivo. Vitamin D and its various metabolites and analogs will be the main secretagogues studied. In addition, we plan to investigate gastrointestinal hormones, pituitary hormones and various other substances. We plan to continue, in a more active fashion, our long-term studies of the mechanism involved in renal osteodystrophy. BIBLIOGRAPHIC REFERENCES: Llach, F., Coburn, J.W., Brickman, A.S., Kurokawa, K., Norman, A.W., Canterbury, J.M., and Reiss, E. Acute action of 1,25-dihydroxyvitamin D3 in normal man: effect on calcium and parathyroid status. J. Clin. Endocrin. Met., 1977 (in press). Lehotay, D.C., Levey, G.S., Canterbury, J.M., Bricker, L.A. and Reiss, E. A peptide inhibitor of glucagon-responsive adenylate cyclase in liver. Glucagon, Piero Foa, ed., Excerpta Medica, Geneva, 1977 (in press).